FBW et al,
May I respectfully suggest that you DON'T turn the transponder to SBY when changing squawk.
In modern ATC centre's, selection of SBY will remove your target/data from the screen until the computer has a few sweeps to fit you back into the system. It will continue to track a "live" transponder while the numbers alter in a sort of 'memory' mode while the squawk changes to look for a new number and database reference.
Thus, if the centre is not one which processes raw data [and few do these days outside a TMA], you can very inconveniently disappear off the screen on selection of SBY.
Is that what you or the ATCO looking after your interests really want??
G'day